1. Field of the Invention
The present invention relates to a system, method and apparatus for performing earth borehole operations.
2. Description of Prior Art
The use of coiled tubing (CT) technology in oil and gas drilling and servicing has become more and more common in the last few years. In CT technology, a continuous pipe wound on a spool is straightened and injected into a well using a CT injector. CT technology can be used for both drilling and servicing, e.g., workovers.
The advantages offered by the use of CT technology, including economy of time and cost are well known. As compared with jointed-pipe technology wherein typically 30-45 foot straight sections of pipe are threadedly connected one section at a time while drilling the wellbore, CT technology allows the continuous deployment of pipe while drilling the well, significantly reducing the frequency with which such drilling must be suspended to allow additional sections of pipe to be connected. This results in less connection time, and as a result, an efficiency of both cost and time.
However, the adoption of CT technology in drilling has been less widespread than originally anticipated as a result of certain problems inherent in using CT in a drilling application. For example, because CT tends to be less robust than jointed-pipe for surface-level drilling, it is often necessary to drill a surface hole using jointed-pipe, cement casing into the surface hole, and then switch over to CT drilling. Additionally, when difficult formations such as gravel are encountered down-hole, it may be necessary to switch from CT drilling to jointed-pipe drilling until drilling through the formation is complete, and then switch back to CT drilling to continue drilling the well. Similarly, when it is necessary to perform drill stem testing to assess conditions downhole, it may again be necessary to switch from CT drilling to jointed-pipe drilling and then back again. Finally, a switch back to jointed pipe operations is necessary to run casing into the drilled well. In short, in CT drilling operations it is generally necessary for customers and crew to switch back and forth between a CT drilling rig and a jointed-pipe conventional drilling rig, a process which results in significant down-time as one rig is moved out of the way, and the other rig put in place.
Another disadvantage of CT drilling is the time consuming process of assembling a (bottom-hole-assembly (BHA)—the components at the end of the CT for drilling, testing, well servicing, etc.), and connecting the BHA to the end of the CT. Presently, this step is performed manually through the use of rotary tables and make-up/breakout equipment. In some instances, top drives are used but the CT injector and the top drive must be moved out of each others way, i.e., they cannot both be in line with the borehole. Not only does this process result in costly downtime, but it can also present safety hazards to the workers as they are required to manipulate heavy components manually.
To address the problems above associated with the use of CT technology and provide for selective and rapid switching from the use of a CT injector to a top drive operation, certain so-called “universal” or “hybrid” rigs have been developed. Typical examples of the universal rigs, i.e., a rig which utilizes a single mast to perform both top drive and CT operations, the top drive and the CT injector being generally at all times operatively connected to the mast, are shown in United States Patent Publication 2004/0206551; and U.S. Pat. Nos. 6,003,598, and 6,609,565. Thus, in U.S. Publication 2004/0206551 there is disclosed a rig adapted to perform earth borehole operations using both CT and/or jointed-pipes, the CT injector and a top drive being mounted on the same mast, the CT injector being selectively moveable between a first position wherein the CT injector is in line with the mast of the rig and hence the earth borehole and a second position wherein the CT injector is out of line with the mast and hence the earth borehole.
In all of the systems disclosed in the aforementioned patents, publications and the cross-referenced related applications, the reel of CT and the CT injector are on or are carried by the same carrier. Heretofore in CT operations particularly drilling, well depth has been limited to about 2200 meters because of governmental regulations regarding the weight and/or height of loads moving on highways. A CT injector can weigh from 20,000 to 40,000 lbs depending upon its size. As to the CT itself, 2200 meters of 3½″ CT, including the reel upon which it is wound can weigh from 60,000 to 80,000 lbs. Thus, because of governmental regulations regarding weight that can be transported on highways, reels of 3½″ CT exceeding about 2200 meters cannot be transported on most highways since the combined weight of the CT and the CT injector would exceed the weight limitations. Clearly it is possible to transport greater lengths of smaller diameter, e.g., 2⅞″ CT. However, particularly in using CT to conduct drilling operations at depths of about 2200 meters, the hydraulics of fluid flow, e.g., flow of drilling mud, dictate that the CT be 3½″ or greater in diameter.
In prior art CT systems wherein a reel or spool of CT is mounted on a carrier, the spool is positioned on the carrier such that the core on which the CT can be wound does not extend for the maximum width of the carrier. This is because the drive assembly used to rotate the spool is on the side of the spool meaning that the drive assembly takes up some of the lateral spacing between the opposed sides of the CT carrier. Since this reduces the overall length of the spool and hence the length of the winding core, less CT can be wound upon the spool in these prior art systems.